Motor-driven pump for delivering liquids at a pressure substantially constant and independent from the delivery

ABSTRACT

A PISTON PUMP WHICH DELIVERS LIQUIDS AT A PRESSURE CONSTANT AND INDEPENDENT FROM THE QUANTITY DELIVERED. THE PUMP COOPERATES WITH A CONTROL UNIT WHICH ALLOWS AUTOMATIC VARIATION OF THE PISTON STROKE WITH CHANGE OF DELIVERY, BUT WITHOUT SUBSTANTIAL CHANGE OF DISCHARGE PRESSURE. THIS STROKE VARIATION IS PERFORMED BY MEANS OF A YIELDING LIQUID CONNECTION BETWEEN THE PISTON PER-   FORMING THE SUCTION STROKE AND THE PISTON PERFORMING THE DELIVERY STROKE. THE DRIVE IS RESILIENTLY COUPLED WITH THE PISTONS DURING THE SUCTION STROKE SO THAT PARTIAL STORKES ARE PERFORMED WITH A PARTIAL IDLING DRIVE.

MOTOR-DRIVEN PUMP FOR DELIVERING LIQUIDS ATA PRESSURE SUBSTANTIALLY CONSTANT AND INDEPENDENT FROM THE DELIVERY Filed Aug. 21. 1968 Fi 1, L5 F/ z.

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4 Sheets-Sheet 1 4 O 6 llllllllllll Jan. 19, 1971 H. scHEFFE 3,556,690

MOTOR-DRIVEN PUMP FOR DELIVERING LIQUIDS AT A PRESSURE SUBSTANTIALLY CONSTANT AND INDEPENDENT Filed Aug. 21, 1968 FROM THE DELIVERY 4 Sheets-Sheet 2 IlllllllllllIIIIIIIIII'] M II l I 64 INVENTOR MOTOR-DRIVEN PUMP FOR DELIVERING LIQUIDS AT A PRESSURE SUBSTANTIALLY CONSTANT AND INDEPENDENT Filed Aug. 21. 1968 FROM THE DELIVERY -4 Sheets-Sheet 3 Fig.5.

Fig. 6.

INVENTOR Jan. 19, 1971 'SCHEFFER I 3,556,690

1 H MOTOR-DRIVEN PUMP FOR DELIVERING LIQUIDS AT A-PHESSURE SUBSTANTIALLY CONSTANT AND INDEPENDENT Filed Aug. 21. 1968 THE DELIVERY 4 Sheets-Sheet 4 3,556,690 MOTOR-DRIVEN PUMP FOR DELIVERING LIQUIDS AT A PRESSURE SUBSTANTIALLY CONSTANT AND INDEPENDENT FROM THE DELIVERY Harry Schelfer, Brackwede, Germany, assignor to Harry Kruger GmbH, Brackwede, Germany Filed Aug. 21, 1968, Ser. No. 754,345 Claims priority, application Germany, Oct. 2, 1967,

3,497 Int. Cl. F04b 21/02, 23/04, 37/00 US. Cl. 417--471 8 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION The invention relates to a motor-driven pump for delivering liquids at a pressure substantially constant and independent from the quantity delivered per second, especially for lacquers and other substances for surface coating applying the airless process, i.e., without application of compressed air in the atomizing step.

Up to now, compressed air-operated pressure transmitters have been used for this purpose, because in the airless process one of the main prerequisites is a constantly available pressure independent from the quantity delivered per second. The low overall efficiency of a compressedair operated airless apparatus, as well as the dependence from air compressor plants, make the construction of directly motor-driven high-pressure pumps appear to be suitable in this application field. Beside the control of the quantity delivered per second independent from pressure already mentioned, the new pump must also allow an adjustable working pressure.

SUMMARY OF THE INVENTION In accordance with the invention, the problem is solved in that at least two freely displaceably arranged pistons are connected on the one side, with a common control chamber filled with a liquid pressurized by pressure means and, on the other side, are connected each via a suction and pressure valve with a suction line and a delivery line, and the delivery stroke of these pistons is performed by action from the control chamber side and their suction stroke is performed via a one-way connection from a driving source in such a manner that the drive pulses for the suction strokes of the pistons are uniformly distributed over a complete cycle of movement of the pistons. In this manner, the pistons always perform a stroke at a time which corresponds to the respective delivery. When this quantity drops to zero, the strokes performed by the piston also will be equal to zero. In this arrangement, the drive shaft continues to move making use of the one-way connections between the drive means and the piston.

Upon reduction of the quantity delivered per second the pressure means pressurizing the liquid in said control chamber will correspondingly reduce, however, con- United States Patent O Patented Jan. 19, 1971 stantly securing the delivery pressure while the respective quantity of deliverytcorresponds to the quantity of control liquid which is displaced in the control chamber by the piston performing the suction stroke to the cylinder of the other piston; thereby the other piston is indirectly driven to perform, its delivery stroke.

in principle, the driving method for the plurality of pistons provided in accordance with the invention is of no importance. More than two, for instance, three or four pistons may be provided. It is also possible, for example, to use several motors which drive synchronously the pistons in the manner indicated and in dephased order with respect to each other. It is also possible to provide several shafts driven by one motor, the synchronous running of which is secured by interposed gears. As a rule, however, it will be recommendable to drive the pistons to perform their suction stroke by means of one common shaft driven by a motor.

Preferably, two pistons are provided which are driven in opposite directions at a time by means of two eccentric cams arranged on the shaft, said cams being dephased with respect to each other through 180.

Further improvements and suitable modifications of the invention are described by way of the enclosed drawing which shows some examples of embodiments of the invention in a schematic representation.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows a longitudinal sectional view of a high pressure pump constructed in accordance with the invention,

FIG. 2 shows a partially sectional side view of the pump taken on line 11-11 of FIG. 1,

FIG. 3 shows a longitudinal sectional view of a second embodiment of a high pressure pump designed in accordance with the invention,

FIG. 4 shows a partially sectional side view of the pump of FIG. 3 taken on line IVIV of FIG. 3,

FIG. 5 a longitudinal sectional view of a third embodiment of a pump constructed in accordance with the present invention,

FIG. 6 a partially sectional view taken on line VIVI of FIG. 5,

FIG. 7 a longitudinal sectional view of a fourth embodiment of the invention, and

FIG. '8 a partially sectional side view taken on line VIIIVIII of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With the embodiments in accordance with FIGS. 1 and 2, the eccentric shaft 2 is rotatably supported in ball bearings 3 provided in the crankcase '1. The driving motor proper is not shown. Eccentric cams are angularly offset from each other through the crankcase 1 is fixed to the pump casing 4; the eccentric cams 110 act on the differential piston 13 via piston rods 11 and cup springs 12. In the piston rod guides 14, there are disposed O-rings '15. The gaskets 16 and 18 are put under stress by means of springs 17 and seal the pump against the flow medium; the leakage chambers 19 are provided with O-rings 20 inside. The gaskets 2 1 are supported against a COntrOl cylinder 51 by brushes 22. In the control cylinder 51, a control piston 52 is sealed by means of an O-ring 53 which closes a control chamber 102 into which the two differential pistons 13 are received. The piston 52 contains an excess-pressure valve 54 and the refilling valve 55. Cup springs 56 are disposed above the piston 52 which are supported by an adjusting screw 58 via a pressure plate 57, said screw 58 being screwed into the cover 59 of the control cylinder 51. The filler connections 5 permit the introduction of a rinsing or cleaning liquid, the drain of which is prevented by the closure screws 6. The suction valve 23 and the pressure valves 24 open into a common suction line 100 and a common pressure line .101, respectively. The pistons 13 are composed of a piston portion 105 with large cross section and a piston portion 106 with small cross section. The effective annular surface between both portions is located in a working chamber 107.

In the embodiment shown in FIGS. 3 and 4, the pump proper is the same as compared with that shown in FIG. 1 and 2 so that like reference numerals have been used for like parts. The control unit, however, is different. A control housing 61 is fastened on the pump casing 4. A control piston 66 is sealed by an O-ring 67 against a bore disposed in the control housing 61, said control piston closing a control cylinder 103 which may be filled at its upper portion with a pressurized gas. An adjusting piston 62 is sealed by an O-ring 63 against a second cylinder disposed in the control housing 61 and connected to the control chamber 102; the adjusting piston contains an excess-pressure valve 64 and the refilling valve 65 and is supported by means of an adjusting screw 68 rotatably arranged in the cover 69.

In the embodiment according to the FIGS. 5 and 6 the high pressure pump is again unchanged and is identified by the same reference numerals. In the pump casing 4, however, there is additionally disposed an adjusting piston 72 sealed the control chamber 102 by means of O-ring 73, the movement of said piston 72 being limited on one side by means of an adjusting screw 78. The adjusting piston 72 is under the influence of the pressurized liquid delivered by the pump via conduit 104. It is also possible to use another pressure medium. The filler connection 5 for the rinsing liquid is arranged in a somewhat different position as compared with the embodiments shown in FIGS. 1 to 4. A control cylinder with a control piston 76 is disposed on the pump casing 4, said control piston 76 separating the gas chamber 103 against the control chamber 102 by means of an O-ring 77. The control cylinder cover 79 closes the control cylinder at the top. An excess-pressure valve 74 and a refilling valve 75 are seated in an annular channel.

In the embodiment shown in FIGS. 7 and 8, the crankcase 99 encloses the crankshaft 98 rotatably supported in ball bearings 97. The crankcase 99 is rigidly connected 'with the pump casing 96. In the two longitudinal bores of the pump casing 96, are disposed the piston rod guides 84, the gaskets 91 and the bushes 92. The piston rods 81 are connected with the crankshaft 98 via the connecting rods 85. The pistons 83 are sealed in the bores of the pump casing 96 by gaskets 88.

The cranks 111 of the shaft 98 drive, via the connecting rods 85, the piston rods guided on a straight line by means of the guides 84. The piston rods 81 may displace the pistons 83 via cup springs 82. The valve case 87 is rigidly and tightly screwed to the pump casing 96. The suction valves 93 and the pressure valves 94 open into a common suction line 100 and a common pressure line 101, respectively. The control chamber 102 is disposed between the gaskets 86 and 88 which chamber is filled, in particular, with oil. The control chamber 102 is in communication with one of the three control units shown in the FIGS. 1 to 6 via a lateral bore 108.

The pump is substantially alike in the embodiments shown in FIGS. 1 to 6. With rotation of the crankshaft the connecting rods 11 are guided upwardly and take along with them the differential pistons 13 via the cup spring 12. Thereby the volume of the working chamber 1107 is expanded between the gaskets 16 and 18; the suction valves 23 open, and the fiow medium to be delivered is drawn in. By the angular offset arrangement of the eccentric cams through 180 it is possible for the first piston 13 to move downward during the upward movement of the second differential piston 13. This downward movement is effected by the upwardly moving second piston due to displacement of the pressurized fluid present above the second differential piston 13 in the control chamber 102, so that the downwardly moving first piston 13 is indirectly driven by the pressure fluid displaced in the control chamber 102. In the downward movement, the ring chamber 107 between the gaskets 16 and 18 is reduced, and a corresponding quantity of flow medium to be delivered is pressed out through the pressure valves 24.

The oil charge above the differential pistons 13 reaches approximately as far as one half the height of the control cylinder 51, with the oil above piston 52 being pressureless. The oil pressure may be adjusted by means of the screw 58 via cup spring 56.

In the case of no or low delivery, both differential pistons 13 move into the upper dead center position and remain there. The excess quantity of oil escapes into the control cylinder 51 and presses the control piston 52 upwardly through a corresponding distance. Due to the ratio of this path to the overall spring path, the pres-- sure increase resulting with lower quantities of delivery per second may be kept within as small limits as may be desired. The piston rods 11 now run empty up and down in the pistons. The refilling valve 55 serves to balance possible leakage losses. The rinsing liquid to be introduced through the tfiller connection 5 makes it possible at any time to recognize the condition of the gaskets 16. 18 and 20.

The operation of the control unit shown in FIGS. 3 and 4 is similar to that shown in FIGS. 1 and 2. The cup spring 56 is replaced by a gas filling the control cylinder 103 above control piston 66 to which gas filling, if desired or required, may be given a precompression. The pressure adjustment is effected via an adjusting piston 62 by means of a screw 68. With no or partial output, the displaced oil volume will increase the pressure of the gas included above the piston 66 in control cylinder 103.

The control with the embodiment shown in FIGS. 5 and 6 takes place in a similar manner as shown in FIGS. 3 and 4, however, with the exception that for the generation of higher pressures the adjusting piston 72 is adjusted by means of a servo effect of the flow medium to be delivered. A gas may be present in control cylinder 103 above the control piston 76 which gas is precompressed if desired or required. The underside of the adjusting piston 72 is under action of the flow medium to be delivered through a small bore 104 provided downstream of the pressure valves 24.

By the selection of a suitable ratio of the piston surfaces on one side exposed to chamber 107 with the flow medium pressure acting thereon and on the other side at chamber 102 with the oil pressure acting thereon the pressure of the flow medium to be delivered may be higher than that of the oil in the control chamber 102, so that, when the adjusting screw 78 is screwed higher, the adjusting piston 72 is urged upwardly thereby increasing the gas pressure in control cylinder 103 above the control piston 76, which in turn causes an increase of the oil pressure in the control chamber 102 and therewith also of the discharge pressure. A decrease in pressure may take place under reverse conditions.

With all three control modifications, the full pressure is always available while the performance delivered from the crank shaft corresponds only to the actual delivery. With partial output of flow medium, the strokes of the differential pistons 13 are also performed only partially.

The principle used with the embodiment shown in FIGS. 7 and 8 is the same as in the FIGS. 1 to 6 with the exception that instead of a compression driving movement, a tension driving movement has been selected. In this operation, the rotation of the crankshaft 98 is acting via the connecting rods and the piston rods 81 on the cup spring 82 and thus on the pistons 83.

The medium to be delivered is sucked in through the suction valve 93 up to the gaskets 91 and is pumped through the pressure valves 94. The advantage of this embodiment especially resides in that the delivery part is separated from the control and driving units of the pump by only one rinsing medium chamber which may be charged through the filler connection 95. The cost of manufacture of the driving mechanism is somewhat higher with this embodiment. Also in this embodiment, the pistons 83 follow the movements of the piston rods 81 only so far as is admitted by the output of the medium to be delivered. A correspondingly large space has been left free in the pistons 83 below the piston rods 81 for the necessary idle stroke. The control takes place exactly as with the embodiments shown in FIGS. 1 to 6.

With the embodiments according to FIGS. 1 to 6, the full large front areas of the pistons 13 extend into the oilfilled control chamber 102, while in the working chambers 107 the smaller annular surfaces are under the action of the flow medium. With the embodiment in accordance with FIGS. 7 and 8, a larger diameter piston 109 is provided on the piston 83 which is sealed by the gasket 88. The annular surfaces between the pistons 83 and 109 is larger than the surface of the piston 83. As the annular surface is effective in the control chamber 102 and the surface of the piston member 83 is effective in the working chamber 107, here as well as with the embodiments according to FIGS. 1 to 6, a pressure transformation takes place in such a manner that the pressure downstream from the pressure valves is greater than the pressure in the control chamber.

In the case of other embodiments it may be suitable to invert the ratio of the piston surfaces so that the pressure in the control chamber 102 is greater than the pressure in the delivery line 10 1.

A special advantage of the subject matter of this invention consists in that the control chamber is completely separated from the working chamber. The liquids and suspensions which are delivered when performing the airless process, for instance paints etc., are compounded to a considerable extent with solids, for instance, solid pigments which may be exert considerable wearing and abrasive effects. Also the pressures are rather high and lie, for example, in the order of 150 kg./cm. Under these circumstances, it will have an especially favourable effect that the control chamber has no connection or contact with the medium to be delivered but is filled with a hydraulic oil of a suitable composition.

What I claim is:

1. A pump characterized by its ability to pump variable quantities of liquids at a substantially constant pressure comprising, in combination, a pump casing, at least first and second piston-receiving cylinders defined in said casing, first and second pistons axially slidably received within said first and second cylinders, respectively, said cylinders each being defined by a first chamber and a second chamber axially spaced from said first chamber, [first and second pressure faces defined upon each piston sealingly located within said first and second chamber of the associated cylinder, respectively, said faces of a common piston being disposed in opposite axial directions with respect to the axis of the associated piston, liquid supply passage means communicating with said first chambers, a common liquid discharge passage means communicating with said first chambers, check valve means located in said supply and discharge passage means, alternating direction producing power driven drive means, first and second piston rod means in driven engagement with said drive means, lost motion means interposed between said first and second piston rod means and said tfirst and second pistons, respectively, for selectively axially and alternately moving said pistons in the axial direction to produce a suction stroke under the influence of said drive means and draw liquid into said first chambers, means defined in said casing establishing communication between said second chambers and said second pressure faces, a liquid accumulator communicating with said second chambers, and biasing means associated with said accumulator imposing a predetermined pressure on liquid therein whereby the pressure acting on the liquid within said accumulator and second chambers and imposed on said second pressure faces solely produces the force on said pistons to axially move said pistons in the direction which produces pressurization of the liquid within said first chambers.

2. A pump in accordance with claim 1, wherein said drive means includes a rotatable shaft, and eccentric drive surfaces defined on said shaft adapted to engage said piston rods.

3. A pump in accordance with claim 2, wherein two pistons are located in said casing and two eccentric drive surfaces are defined on said shaft angularly displaced approximately with respect to each other.

4. A pump in accordance with claim 1, wherein said lost motion means include springs interposed between said piston rods and said pistons.

5. In a pump as in claim 1, wherein said accumulator includes volume adjustment means for varying said predetermined pressure of said accumulator and varying the pressurization of the liquid within said first chambers.

6. In a pump as in claim 5, wherein said volume adjustment means comprises a variable volume chamber communicating with said accumulator, and adjustable volume means within said variable volume chamber.

7. In a pump in accordance with claim 1, wherein said tfirst and said second piston pressure faces have different effective areas whereby a pressure differential exists be tween said second chambers and said first chambers during pressurization of said first chambers by the liquid pressure acting upon said second faces.

8. In a pump in accordance with claim 7, wherein the area of said first faces of said pistons are larger than the area of said second faces.

References Cited UNITED STATES PATENTS 3,314,365 4/1967 Ritchie 10'338 1,891,771 12/1932 Mondenhall et al. 103170 2,145,854 2/1939 Bijur 10338 2,417,474 3/1947 Feroy 103-38 2,437,887 3/1948 Mott 103l62 2,936,588 5/1960 Gerpen 103-38 3,016,843 1/1962 Smith 103l70 3,398,691 8/1968 Sato et al 10338 3,257,952 1/1966 McCormick l0344 3,340,818 9/1967 Schanzlin 103-l78 FOREIGN PATENTS 774,701 6/ 196 5 Great Britain 103l69 WILLIAM L. FREEH, Primary Examiner US Cl. X.R. 

